U.S. Attorney General Jeff Sessions on Tuesday strongly denied alleged involvement in any collusion with Russia during last year's Donald Trump campaign, calling it an "appalling and detestable lie."

"The suggestion that I participated in any collusion or that I was aware of any collusion with the Russian government to hurt or to undermine the integrity of our democratic process, is an appalling and detestable lie," he told lawmakers when testifying before the U.S. Senate Intelligence Committee.

"Not one thing happened that was improper" in his two meetings with Russian Ambassador Sergey Kislyak during the 2016 campaign, said Sessions, who was then an Alabama senator and a close Trump advisor.

Sessions also denied that he had a third, unreported meeting with the Russian ambassador during the campaign that made Trump U.S. president.

"I have never met with or had any conversations with any Russians or any foreign officials concerning any type of interference with any campaign or election in the United States," the Trump's top lawyer said.

"Further, I have no knowledge of any such conversations by anyone connected with the Trump campaign," he added.

U.S. intelligence agencies have concluded that Russian President Vladimir Putin ordered an effort to interfere in the U.S. presidential election, including hacking and disclosing damaging emails against Trump's rival, Democratic candidate Hillary Clinton.

Russia has denied any such interference, and Trump has denied any collusion with Russia.

During Tuesday's hearing, Sessions also rejected misconduct in the firing of James Comey, director of Federal Bureau of Investigation (FBI), vowing to defend his "honor against scurrilous and false allegations."

Meanwhile, he said it was not improper for Trump to meet with the then FBI chief Comey, but it was improper for Comey to disclose the content of his one-to-one talks with Trump.

The attorney general also said he couldn't confirm or deny private talks he had with Trump regarding Comey's firing.

Last Thursday, Comey told the same Senate panel during a hearing that he was confused over the circumstances under which he was fired on May 9, and said Trump had "hoped" that he would drop the FBI investigation into former National Security Advisor Michael Flynn over alleged collusion with Russia during the Trump campaign.

Trump on Friday denied Comey's accusation, saying that Comey was not speaking the truth regarding several details during his testimony to the Senate.

Comey also said in his testimony that he knew details that made Sessions' involvement in the FBI Russia probe "problematic."

Comey reportedly told lawmakers behind closed doors that the details included a third unreported meeting between Sessions and Russian ambassador Kislyak.

Sessions was forced to recuse himself in March from the federal investigation into possible Russian interference in the U.S. election after media reports said that he twice met with Kislyak during the 2016 campaign and did not disclose that to the Senate during his confirmation hearing in January.

Sessions was the first U.S. senator to publicly support the Trump campaign last year. The probe over possible collusion between the Trump campaign and Russia is now in the hands of special counsel Bob Mueller following Comey's dismissal.